The iron sulfur protein, FNR (fumarate nitrate reduction) is a global gene regulator, controlling the transcription of more than 100 genes whose products facilitate the adaptation of Eschericia coli for growth under oxygen limiting conditions. Studies have shown that the four iron-four sulfur cluster is converted into a 2 iron-2 sulfur cluster on exposure to oxygen, a process that decreases DNA binding by FNR. Low temperature, liquid nitrogen and liquid helium temperatures, EPR was performed on samples of wild type FNR and a mutant stable to oxidative damage, L28H, that had been treated with nitric oxide. Both samples exhibited the g=2.04 signal attributed to an iron-thiol-dinitrosyl complex. No signals were observed that could be attributed to Fe-S clusters.